The proposed research will continue to study the differentiation of receptors for LH in developing follicles and corpus luteum under defined conditions. Since we have begun to study time dependent localization of radioiodinated hCG in follicles, efforts will be made to characterize initial binding sites, and quantitate its number and pattern of redistribution within individual follicles and follicular cells. This is to be followed by a serial study to localize LH-receptors in luteal cells, during luteinization and luteolysis. In so doing, the ultrastructural characteristics of the developing follicular cells will be correlated with their ability to bind and process radioiodinated hCG. This will be accomplished by electron microscopy, electron microscopic radioautography and cell-fraction studies following the administration of radio-labeled hCG.